1. Field of the Invention
The present invention relates to a deformable mirror system composed of a deformable mirror configured to deform a shape of a reflection surface by using an electrostatic drive and of a deformable mirror drive device for driving the deformable mirror, and to a deformable mirror drive device for use in the system.
2. Description of the Related Art
In recent years, a deformable mirror configured to deform a reflection surface by using electrostatic drive, by applying a, so-called, micro-electro-mechanical system (MEMS) technique using a semiconductor manufacturing technology has been widely noticed.
In such a deformable mirror, it is required for obtaining desired reflection to measure a deformation quantity of the reflection surface. As regards a method for measuring a deformation quantity, a method for measuring a change in capacitance is disclosed; for example, in U.S. Pat. No. 7,190,500.
A deformable mirror disclosed in the U.S. Patent is provided with a flexible thin film and a control electrode. The flexible thin film includes a reflection surface to be deformed by electrostatic attractive force and an upper electrode. The control electrode is an electrode which is arranged facing the thin film and partly works for control and for detecting capacitance. Applying a voltage between the upper electrode and the control electrode generates electrostatic drive force and deforms the reflection surface. A capacitance detection circuit measures capacitance between the upper electrode and the control electrode to calculate the deformation quantity of the reflection surface.
The U.S. Patent discloses the following detection method. The method applies a high voltage from a constant voltage source to the control electrode through a resistor. Here, applying a high-frequency voltage from a high-frequency power source to a capacitance detection electrode that is the control electrode varies potential at the control electrode. These variations are monitored as changes in electric current by means of the capacitance detection circuit through the upper electrode. The capacitance, namely, the deformation quantity of the reflection surface is detected based on a phase and amplitude of the current detect.
The U.S. Patent discloses the foregoing method for detecting the deformation quantity of the reflection surface. However, the U.S. patent does not disclose a way how to control a voltage to be applied between the upper electrode and the control electrode of the deformable mirror by using the detected magnitude of the deformation.
The present invention has been made in consideration of the above point, and an object of the invention is to provide a deformable mirror system and a deformable mirror drive device which are configured to precisely drive a deformable mirror by detecting the deformation quantity of a reflection surface and by controlling the voltage to be applied between electrodes by using the detected deformation quantity.